The emerging biomolecular role of vitamin D in skeletal muscle

Evaluation of Nutrition and Performance Parameters in Division 1 Collegiate Athletes

BACKGROUND

Testing and evaluating athletes is necessary and should include performance, body composition, and nutrition. The purpose of this study was to report assessments of dietary intake, V˙O2max, and body composition in D1 collegiate athletes and examine relationships between these assessments.

METHODS

Dietary intake was assessed with 3-day recalls and compared to recommendations, and body composition was assessed via bioelectrical impedance analysis (BIA) (n = 48). V˙O2max was evaluated using a graded exercise test (GXT) with a verification bout (n = 35). Reliability between "true" V˙O2max and verification was determined. Correlations and regressions were performed.

RESULTS

Energy, carbohydrate, and micronutrient intake was lower than recommendations. Mean V˙O2max was 47.3 and 47.4 mL·kg-1·min-1 for GXT and verification, respectively. While correlations were apparent among dietary intake, V˙O2max, and body composition, percent fat-free mass (%FFM) predicted 36% of V˙O2max.

CONCLUSIONS

Collegiate athletes are not meeting energy and carbohydrate recommendations and exceed fat recommendations. Vitamin D and magnesium were low in all sports, and iron and calcium were low in females. V˙O2max ranged from 35.6 to 63.0 mL·kg-1·min-1, with females below average and males meeting typical values for their designated sport. Assessing D1 athletes can provide guidance for sports dietitians, coaches, and strength and conditioning specialists to track and monitor nutrition in athletes.

Biological basis and treatment of frailty and sarcopenia

In an ageing society, the importance of maintaining healthy life expectancy has been emphasized. As a result of age-related decline in functional reserve, frailty is a state of increased vulnerability and susceptibility to adverse health outcomes with a serious impact on healthy life expectancy. The decline in skeletal muscle mass and function, also known as sarcopenia, is key in the development of physical frailty. Both frailty and sarcopenia are highly prevalent in patients not only with advanced age but also in patients with illnesses that exacerbate their progression like heart failure (HF), cancer, or dementia, with the prevalence of frailty and sarcopenia in HF patients reaching up to 50-75% and 19.5-47.3%, respectively, resulting in 1.5-3 times higher 1-year mortality. The biological mechanisms of frailty and sarcopenia are multifactorial, complex, and not yet fully elucidated, ranging from DNA damage, proteostasis impairment, and epigenetic changes to mitochondrial dysfunction, cellular senescence, and environmental factors, many of which are further linked to cardiac disease. Currently, there is no gold standard for the treatment of frailty and sarcopenia, however, growing evidence supports that a combination of exercise training and nutritional supplement improves skeletal muscle function and frailty, with a variety of other therapies being devised based on the underlying pathophysiology. In this review, we address the involvement of frailty and sarcopenia in cardiac disease and describe the latest insights into their biological mechanisms as well as the potential for intervention through exercise, diet, and specific therapies.

Skeletal Muscle Injury in Chronic Kidney Disease-From Histologic Changes to Molecular Mechanisms and to Novel Therapies

Chronic kidney disease (CKD) is associated with significant reductions in lean body mass and in the mass of various tissues, including skeletal muscle, which causes fatigue and contributes to high mortality rates. In CKD, the cellular protein turnover is imbalanced, with protein degradation outweighing protein synthesis, leading to a loss of protein and cell mass, which impairs tissue function. As CKD itself, skeletal muscle wasting, or sarcopenia, can have various origins and causes, and both CKD and sarcopenia share common risk factors, such as diabetes, obesity, and age. While these pathologies together with reduced physical performance and malnutrition contribute to muscle loss, they cannot explain all features of CKD-associated sarcopenia. Metabolic acidosis, systemic inflammation, insulin resistance and the accumulation of uremic toxins have been identified as additional factors that occur in CKD and that can contribute to sarcopenia. Here, we discuss the elevation of systemic phosphate levels, also called hyperphosphatemia, and the imbalance in the endocrine regulators of phosphate metabolism as another CKD-associated pathology that can directly and indirectly harm skeletal muscle tissue. To identify causes, affected cell types, and the mechanisms of sarcopenia and thereby novel targets for therapeutic interventions, it is important to first characterize the precise pathologic changes on molecular, cellular, and histologic levels, and to do so in CKD patients as well as in animal models of CKD, which we describe here in detail. We also discuss the currently known pathomechanisms and therapeutic approaches of CKD-associated sarcopenia, as well as the effects of hyperphosphatemia and the novel drug targets it could provide to protect skeletal muscle in CKD.

Seasonal Variation in Vitamin D Status Does Not Interfere with Improvements in Aerobic and Muscular Endurance in Conscripts during Basic Military Training

Considering a lack of respective data, the primary objective of this study was to assess whether seasonal variation in vitamin D status (D-status) affects the extent of improvement in physical performance (PP) in conscripts during basic military training (BMT). D-status, PP and several blood parameters were measured repeatedly in conscripts whose 10-week BMT started in July (cohort S-C; n = 96) or in October (cohort A-C; n = 107). D-status during BMT was higher in S-C compared to A-C (overall serum 25(OH)D 61.4 ± 16.1 and 48.5 ± 20.7 nmol/L, respectively; p < 0.0001). Significant (p < 0.05) improvements in both aerobic and muscular endurance occurred in both cohorts during BMT. Pooled data of the two cohorts revealed a highly reliable (p = 0.000) but weak (R2 = 0.038-0.162) positive association between D-status and PP measures both at the beginning and end of BMT. However, further analysis showed that such a relationship occurred only in conscripts with insufficient or deficient D-status, but not in their vitamin D-sufficient companions. Significant (p < 0.05) increases in serum testosterone-to-cortisol ratio and decreases in ferritin levels occurred during BMT. In conclusion, a positive association exists between D-status and PP measures, but seasonal variation in D-status does not influence the extent of improvement in PP in conscripts during BMT.

Skeletal muscle as a molecular and cellular biomarker of disease progression in amyotrophic lateral sclerosis: a narrative review

Amyotrophic lateral sclerosis is a fatal multisystemic neurodegenerative disease with motor neurons being a primary target. Although progressive weakness is a hallmark feature of amyotrophic lateral sclerosis, there is considerable heterogeneity, including clinical presentation, progression, and the underlying triggers for disease initiation. Based on longitudinal studies with families harboring amyotrophic lateral sclerosis-associated gene mutations, it has become apparent that overt disease is preceded by a prodromal phase, possibly in years, where compensatory mechanisms delay symptom onset. Since 85-90% of amyotrophic lateral sclerosis is sporadic, there is a strong need for identifying biomarkers that can detect this prodromal phase as motor neurons have limited capacity for regeneration. Current Food and Drug Administration-approved therapies work by slowing the degenerative process and are most effective early in the disease. Skeletal muscle, including the neuromuscular junction, manifests abnormalities at the earliest stages of the disease, before motor neuron loss, making it a promising source for identifying biomarkers of the prodromal phase. The accessibility of muscle through biopsy provides a lens into the distal motor system at earlier stages and in real time. The advent of "omics" technology has led to the identification of numerous dysregulated molecules in amyotrophic lateral sclerosis muscle, ranging from coding and non-coding RNAs to proteins and metabolites. This technology has opened the door for identifying biomarkers of disease activity and providing insight into disease mechanisms. A major challenge is correlating the myriad of dysregulated molecules with clinical or histological progression and understanding their relevance to presymptomatic phases of disease. There are two major goals of this review. The first is to summarize some of the biomarkers identified in human amyotrophic lateral sclerosis muscle that have a clinicopathological correlation with disease activity, evidence of a similar dysregulation in the SOD1G93A mouse during presymptomatic stages, and evidence of progressive change during disease progression. The second goal is to review the molecular pathways these biomarkers reflect and their potential role in mitigating or promoting disease progression, and as such, their potential as therapeutic targets in amyotrophic lateral sclerosis.

The Effect of Vitamin D Supplementation to Parameter of Sarcopenia in Elderly People: a Systematic Review and Meta-Analysis

Background

Vitamin D plays an essential role in promoting skeletal muscle metabolism. Several studies show that vitamin D may help the elderly prevent sarcopenia. Nevertheless, the outcome remains debatable. Our meta-analysis aimed to summarize the effect of vitamin D supplementation on sarcopenia-related parameters.

Methods

We searched PubMed, Cochrane, Springer, SAGE Journals, and Scopus abstracts on 10th December 2021 for relevant studies. We included articles that studied the effect of vitamin D on muscle mass, muscle strength, and physical performance. The aim was to measure the muscle mass, muscle strength, and physical performance both at baseline and at the end of the intervention.

Results

A total of 6,628 participants from 35 studies were included. Most of the studies used oral vitamin D, whereas only one study used intramuscular injection. The effect of vitamin D supplementation showed no effect on appendicular skeletal muscle mass (SMD = .05 [95% CI, .33 - .44], p = .79). Regarding muscle strength, vitamin D supplementation did not have a significant effect on muscle strength which is handgrip strength (p = .26). Respecting physical performance, vitamin D supplementation did not affect TUG (Timed Up and Go) (p = .45).

Conclusions

Vitamin D supplementation had minimal effect on sarcopenia-related parameters. Further research into understanding the role of Vitamin D in preventing the progressivity of sarcopenia still needs to be explored.

Nutrition Interventions on Muscle-Related Components of Sarcopenia in Females: A Systematic Review of Randomized Controlled Trials

Sarcopenia is a skeletal muscle disease categorized by low muscle strength, muscle quantity or quality, and physical performance. Sarcopenia etiology is multifaceted, and while resistance training is widely agreed upon for prevention and treatment, disease progression is also highly related to poor diet. The incidence of sarcopenia appears sex-specific and may be increased in females, which is problematic because dietary quality is often altered later in life, particularly after menopause. Identifying effective nutrition or supplementation interventions could be an important strategy to delay sarcopenia and related comorbidities in this vulnerable population. This systematic review examined randomized controlled trials (RCTs) of nutrition strategies on muscle-related components of sarcopenia in middle-aged and older females. A protocol was registered (PROSPERO CRD42022382943) and a systematic search of MEDLINE and CINAHL was undertaken. RCTs from 2013 to 2023 that assessed nutrition-only interventions on muscle mass, muscle strength, and physical function in female participants were included. Fourteen RCTs were included based on selection criteria. Study designs and interventions were heterogeneous in supplementation type and amount, age, and duration. Six RCTs reported beneficial effects of protein, Vitamin D, Vitamin D and Magnesium (Mg), and fish oil on muscle protein synthesis, muscle strength, and/or muscle function. Eight studies that examined various protein interventions, VitD alone, Mg alone, and dairy derivatives did not demonstrate any effect. Exercise appeared to modulate results in several studies. Nutrition interventions alone are likely to have a limited but positive effect on muscle-related components of sarcopenia in females. Current evidence suggests that a combination of dietary intervention and exercise is likely to be key to preventing and treating sarcopenia in middle aged and older females and there is a need for well-designed nutrition based studies in this population.

The Physiological Requirements of and Nutritional Recommendations for Equestrian Riders

Equestrian sport is under-researched within the sport science literature, creating a possible knowledge vacuum for athletes and support personnel wishing to train and perform in an evidence-based manner. This review aims to synthesise available evidence from equitation, sport, and veterinary sciences to describe the pertinent rider physiology of equestrian disciplines. Estimates of energy expenditure and the contribution of underpinning energy systems to equestrian performance are used to provide nutrition and hydration recommendations for competition and training in equestrian disciplines. Relative energy deficiency and disordered eating are also considered. The practical challenges of the equestrian environment, including competitive, personal, and professional factors, injury and concussion, and female participation, are discussed to better highlight novelty within equestrian disciplines compared to more commonly studied sports. The evidence and recommendations are supported by example scenarios, and future research directions are outlined.

Current Research on Vitamin D Supplementation against Sarcopenia: A Review of Clinical Trials

Vitamin D plays an important role in skeletal muscle function and metabolism. The aim of this review was A) to discuss the clinical evidence of vitamin D supplementation either alone or combined with other strategies in the prevention of sarcopenia in non-sarcopenic individuals and B) to critically discuss the clinical evidence on the effect of vitamin D combined with other strategies on muscle strength, mass and function in sarcopenic individuals without vitamin D deficiency. Sparse clinical data on non-sarcopenic individuals indicate that vitamin D alone has a subtle beneficial effect on knee extensor strength at doses 880-1600 IU/day without improving handgrip strength or muscle mass. When co-administered with other supplements such as protein, mixed effects appear to prevent the decline of muscle mass, possibly delaying the onset of sarcopenia in non-sarcopenic individuals, at doses of 800-1,000 IU/day over 6-12 weeks. In sarcopenic individuals, vitamin D 100-1,000 IU/day co-supplementation with protein results in increased handgrip strength between 9.8-40.5%. However, there is no strong clinical evidence that vitamin D dosage correlates with changes in muscle strength or mass. Potential sources of discrepancy among studies are discussed. Future studies with appropriate experimental design are essential to dissect the net effect of vitamin D on sarcopenia.

Interaction of estradiol and vitamin D with low skeletal muscle mass among middle-aged and elderly women

BACKGROUND

Since the connection between muscle atrophy and vitamin D and estradiol status ambiguous, this study was thus conducted to determine whether low skeletal muscle mass (SMM) in middle-aged and elderly women was affected by estradiol and vitamin D levels together.

METHODS

Baseline data from a sub-cohort of the China Northwest Natural Population Cohort: Ningxia Project (CNC-NX) were analyzed. Serum 25-hydroxyvitamin D (25(OH) D) and estradiol were measured by chemiluminescence immunoassay analyzer. Bivariate logistic regression and multiplicative interaction analyses were used to assess the impact of estradiol level and vitamin D status on low SMM, as well as the combined impact of estradiol and low vitamin D status on low SMM.

RESULTS

A total of 287 (9.49%) participants had low SMM, which had lower levels of estradiol and vitamin D concentration than normal SMM group. While, after adjusting the confounding variables, these correlations were maintained in estradiol Q1, Q2, Q3 and vitamin D Q1. Furthermore, the significant combined effect of the highest quartile of estradiol concentrations and non-vitamin D deficiency, and interactions between vitamin D Q1 and estradiol Q2, vitamin D Q1 and estradiol Q3, vitamin D Q2 and estradiol Q1, vitamin D Q3 and estradiol Q3 on low SMM were stably reflected (P for interaction < 0.05).

CONCLUSIONS

Estradiol and vitamin D were interrelated with low SMM in middle-aged and elderly women. Combination of estradiol and vitamin D supplements should be encouraged for middle-aged and elderly women who are at risk of muscle atrophy or experiencing muscle atrophy.

Relationship of Serum 25-Hydroxyvitamin D Levels With Sarcopenia and Body Composition in Community-Dwelling Older Adults: A Paired Case-Control Study

OBJECTIVE

Sarcopenia is a leading health problem among older adults. However, few studies have explored the relationship between serum 25-hydroxyvitamin D [25(OH)D] levels, sarcopenia, and body composition in older Chinese individuals. The aim of this study was to investigate the relationship of serum 25(OH)D levels with sarcopenia, sarcopenia indices, and body composition in community-dwelling older Chinese adults.

DESIGN

Paired case-control study.

SETTING AND PARTICIPANTS

This case-control study enrolled 66 older adults newly diagnosed with sarcopenia (sarcopenia group) and 66 older adults without sarcopenia (non-sarcopenia group) after screening in the community.

METHODS

The definition of sarcopenia was based on the Asian Working Group for Sarcopenia 2019 criteria. Serum levels of 25(OH)D were measured using an enzyme-linked immunosorbent assay. Conditional logistic regression analysis was performed to estimate odds ratios (ORs) and 95% CIs. Spearman's correlation was used to examine the correlations among sarcopenia indices, body composition, and serum 25(OH)D.

RESULTS

Serum 25(OH)D levels were significantly lower in the sarcopenia group (29.08 ± 15.11 ng/mL) than in the non-sarcopenia group (36.28 ± 14.68 ng/mL) (P < .05). Vitamin D deficiency was associated with an increased risk of sarcopenia (OR, 7.749; 95% CI, 1.955-30.714). Serum 25(OH)D levels in men were positively correlated with skeletal muscle mass index (SMI) (r = 0.450; P < .001) and negatively correlated with gait speed (r = -0.282; P = .032). Serum 25(OH)D levels in women were positively correlated with SMI (r = 0.286; P < .001), skeletal muscle mass (r = 0.395; P < .001), and fat-free mass (r = 0.412; P < .001).

CONCLUSIONS AND IMPLICATIONS

Serum 25(OH)D levels were lower in older adults with sarcopenia than those in adults without sarcopenia. Vitamin D deficiency was associated with increased risk of sarcopenia, and serum 25(OH)D levels were positively correlated with SMI.

The association of vitamin D supplementation and serum vitamin D levels with physical activity in older adults: Results from a randomized trial

BACKGROUND

To assess whether vitamin D3 supplementation attenuates the decline in daily physical activity in low-functioning adults at risk for falls.

METHODS

Secondary data analyses of STURDY (Study to Understand Fall Reduction and Vitamin D in You), a response-adaptive randomized clinical trial. Participants included 571 adults aged 70 years and older with baseline serum 25(OH)D levels of 10-29 ng/mL and elevated fall risk, who wore a wrist accelerometer at baseline and at least one follow-up visit and were randomized to receive: 200 IU/day (control), 1000, 2000, or 4000 IU/day of vitamin D3 . Objective physical activity quantities and patterns (total daily activity counts, active minutes/day, and activity fragmentation) were measured for 7-days, 24-h/day, in the free-living environment using the Actigraph GT9x over up to 24-months of follow-up.

RESULTS

In adjusted models, physical activity quantities declined (p < 0.001) and became more fragmented, or "broken up", (p = 0.017) over time. Supplementation with vitamin D3 did not attenuate this decline. Changes in physical activity were more rapid among those with baseline serum 25(OH)D <20 ng/mL compared to those with baseline 25(OH)D levels of 20-29 ng/mL (time*baseline 25(OH)D, p < 0.05).

CONCLUSION

In low-functioning older adults with serum 25(OH)D levels 10-29 ng/mL, vitamin D3 supplementation of 1000 IU/day or higher did not attenuate declines in physical activity compared with 200 IU/day. Those with baseline 25(OH)D <20 ng/mL showed accelerated declines in physical activity. Alternative interventions to supplementation are needed to curb declines in physical activity in older adults with low serum 25(OH)D.

Does vitamin D affect strength and speed characteristics and testosterone concentration in elite young track and field athletes in the North European summer?

BACKGROUND

Currently there are no data examining the relationship between the serum concentration of vitamin D bio-chemical marker 25(OH)D and strength and speed characteristics in elite young track and field athletes. Moreover, there are currently no data examining the correlation of vitamin D status with testosterone concentration in elite young track and field athletes. In studies involving members of the general population and athletes from other sports, conflicting data have been reported.

MATERIAL AND METHODS

Athletes (n = 68) from both genders took part in this study. Male athletes (n = 23) with mean ± SD age of 18.2 ± 1.9 years and female athletes (n = 45) with mean ± SD age of 17.3 ± 2.6 years participated. All athletes were ranked in the Top-3 in their respective age group and their corresponding results were listed in the Top-20 European records according to https://www.tilastopaja.eu/ in 2021.

RESULTS

The average 25(OH)D concentration was 36.5 ± 10.8 ng/mL and 37.8 ± 14.5 ng/mL in male and female athletes respectively. The prevalence of 25(OH)D deficiency (below 20 ng/ml) in both genders was only 5.8%. In the whole group, only 27.9% of athletes had 25(OH)D concentrations between 20 and 30 ng/ml, while 66.2% of athletes had concentrations above 30 ng/ml. There was no difference in vitamin D status between male and female athletes. There was no statistically significant Kruskal-Wallace test correlation between 25(OH)D concentration and performance in the 20 m and 30 m sprint, counter-movement jump and broad jump. There was no correlation between serum concentrations of 25(OH)D and total testosterone in either male or female athletes.

CONCLUSION

In elite young track and field athletes who permanently live and train in an area above 50° north latitude, the prevalence of vitamin D deficiency in the summer months was much lower than in previously published studies examining an athletic population, that may be related to the training process. In this specific group of athletes, no correlation was found between serum 25 (OH) D concentration and strength and speed characteristics or total testosterone concentration.

Associations of serum 25(OH)D levels with physical performance and anabolic hormones in young men

Purpose: The present study examined the association of vitamin D measured by serum 25(OH)D with physical performance outcomes and serum levels of anabolic hormones in young men. Methods: 412 young men (age 19 ± 1 year) entering their compulsory military service volunteered to participate in the study. The study consisted of two groups from two different military bases: Group A was studied in January and group B in July. The groups were first compared with each other and due to statistically significant (p < 0.001 analyzed with independent samples t-test) differences in physical condition (sit-up, push-up, and standing long jump-tests and testosterone levels) between the groups, groups were analyzed separately. The serum levels of 25(OH)D, testosterone (TES), sex hormone binding globulin (SHBG), and insulin-like growth factor-1 (IGF-1) were analyzed by electrochemiluminescence immunoassay. Physical performance tests consisted of muscular fitness (sit-ups, push-ups, standing long jump) and aerobic fitness (12-minute-running) tests. The association of serum 25(OH)D with physical performance tests and anabolic hormones was analyzed using linear regression. Results: After controlling for the group, body mass index, and leisure-time physical activity, serum 25(OH)D level was positively associated with aerobic and muscular fitness (β = 0.15-0.20, all p < 0.05). Also, the participants with sufficient serum 25(OH)D levels (≥75 nmol/L) had better aerobic and muscular fitness and higher TES in group B, and better upper extremity muscular fitness in group A (all p < 0.05). In group A, there were 166 participants with serum levels of 25(OH) D < 75 nmol/L and 18 ≥ 75 nmol/L. In group B, the amounts were 92 (<75 nmol/L) and 136 (≥75 nmol/L), respectively. Conclusion: Serum 25(OH)D was positively associated with both aerobic and muscular fitness and those with sufficient vitamin D levels, had higher levels of TES. Thus, maintaining a sufficient serum 25(OH)D level may be beneficial for physical performance and anabolic state in young men.

Muscle plasticity is influenced by renal function and caloric intake through the FGF23-vitamin D axis

Skeletal muscle, the main metabolic engine in the body of vertebrates, is endowed with great plasticity. The association between skeletal muscle plasticity and two highly prevalent health problems: renal dysfunction and obesity, which share etiologic links as well as many comorbidities, is a subject of great relevance. It is important to know how these alterations impact on the structure and function of skeletal muscle because the changes in muscle phenotype have a major influence on the quality of life of the patients. This literature review aims to discuss the influence of a nontraditional axis involving kidney, bone, and muscle on skeletal muscle plasticity. In this axis, the kidneys play a role as the main site for vitamin D activation. Renal disease leads to a direct decrease in 1,25(OH)₂-vitamin D, secondary to reduction in renal functional mass, and has an indirect effect, through phosphate retention, that contributes to stimulate fibroblast growth factor 23 (FGF23) secretion by bone cells. FGF23 downregulates the renal synthesis of 1,25(OH)₂-vitamin D and upregulates its metabolism. Skeletal production of FGF23 is also regulated by caloric intake: it is increased in obesity and decreased by caloric restriction, and these changes impact on 1,25(OH)₂-vitamin D concentrations, which are decreased in obesity and increased after caloric restriction. Thus, both phosphate retention, that develops secondary to renal failure, and caloric intake influence 1,25(OH)₂-vitamin D that in turn plays a key role in muscle anabolism.

Seven-month wintertime supplementation of 1200 IU vitamin D has no effect on hand grip strength in young, physically active males: A randomized, controlled study

Background

Study Design

Methods

Results

Conclusion

An updated clinical prediction model of protein-energy wasting for hemodialysis patients

Background and aim

Protein-energy wasting (PEW) is critically associated with the reduced quality of life and poor prognosis of hemodialysis patients. However, the diagnosis criteria of PEW are complex, characterized by difficulty in estimating dietary intake and assessing muscle mass loss objectively. We performed a cross-sectional study in hemodialysis patients to propose a novel PEW prediction model.

Materials and methods

A total of 380 patients who underwent maintenance hemodialysis were enrolled in this cross-sectional study. The data were analyzed with univariate and multivariable logistic regression to identify influencing factors of PEW. The PEW prediction model was presented as a nomogram by using the results of logistic regression. Furthermore, receiver operating characteristic (ROC) and decision curve analysis (DCA) were used to test the prediction and discrimination ability of the novel model.

Results

Binary logistic regression was used to identify four independent influencing factors, namely, sex (P = 0.03), triglycerides (P = 0.009), vitamin D (P = 0.029), and NT-proBNP (P = 0.029). The nomogram was applied to display the value of each influencing factor contributed to PEW. Then, we built a novel prediction model of PEW (model 3) by combining these four independent variables with part of the International Society of Renal Nutrition and Metabolism (ISRNM) diagnostic criteria including albumin, total cholesterol, and BMI, while the ISRNM diagnostic criteria served as model 1 and model 2. ROC analysis of model 3 showed that the area under the curve was 0.851 (95%CI: 0.799-0.904), and there was no significant difference between model 3 and model 1 or model 2 (all P > 0.05). DCA revealed that the novel prediction model resulted in clinical net benefit as well as the other two models.

Conclusion

In this research, we proposed a novel PEW prediction model, which could effectively identify PEW in hemodialysis patients and was more convenient and objective than traditional diagnostic criteria.

Association between vitamin D3 levels and frailty in the elderly: A large sample cross-sectional study

Background

Frailty is recognized as a cornerstone of geriatric medicine. Accurately screening and identifying frailty can promote better quality and personalized medical services for the elderly. Previous studies have shown that the association between vitamin D and frailty in the elderly population is still controversial. More research is needed to explore the association between them.

Materials and methods

We used three waves of data from the National Health and Nutrition Examination Survey (NHANES). Based on the widely accepted AAH FRAIL Scale, we measured and evaluated the participants’ frailty from five aspects: fatigue, resistance, ambulation, illness, and loss of weight. All possible relevant variables are included. Machine learning XGboost algorithm, the Least Absolute Shrinkage Selection Operator (LASSO) regression and univariate logistic regression were used to screen variables, and multivariate logistic regression and generalized additive model (GAM) were used to build the model. Finally, subgroup analysis and interaction test were performed to further confirm the association.

Results

In our study, XGboost machine learning algorithm explored the relative importance of all included variables, which confirmed the close association between vitamin D and frailty. After adjusting for all significant covariates, the result indicated that for each additional unit of 25-hydroxyvitamin D3, the risk of frailty was reduced by 1.3% with a statisticaldifference. A smooth curve was constructed based on the GAM. It was found that there was a significant negative correlation between 25-hydroxyvitamin D3 and the risk of frailty.

Conclusion

There may be a negative correlation between 25-hydroxyvitamin D3 and the risk of frailty. However, more well-designed studies are needed to verify this relationship.

Vitamin D is associated with body composition and fat intake, but not with cardiometabolic parameters in adults with obesity

Adults with obesity are at higher risk for developing hypovitaminosis D. Some studies suggest that reduced levels of serum 25-hydroxyvitamin D (25(OH)D) may also be related to disorders in cardiometabolic parameters. However, because of the association between 25(OH)D and obesity, we hypothesized that body composition can be a confounding factor in the association of 25(OH)D with cardiometabolic parameters, and that 25(OH)D is inversely associated with body composition and cardiometabolic parameters and directly associated with fat intake. The aim of this study was to analyze the associations between 25(OH)D with body composition, fat intake, and cardiometabolic parameters in adults with obesity. This cross-sectional study consisted of 52 adults with obesity (61.53% female; 37.50 ± 6.88 years; body mass index [BMI]: 33.60 ± 2.89 kg/m²). Cardiometabolic parameters (fasting blood glucose, insulin resistance index, C-reactive protein, blood pressure, high-density lipoprotein cholesterol, low-density lipoprotein cholesterol, triglycerides, and cholesterol), body mass, BMI, waist circumference, body fat percentage, and fat intake were evaluated. Body mass was negatively associated with 25(OH)D (β = -0.108; P = .048; and R² = 0.090) and BMI (β = -0.621; P = .031; and R² = 0.103), both adjusted for fat intake. 25(OH)D was positively associated with fat intake (β = 0.129; P = .045 and R² = 0.078) adjusted for sex, age, and skin color. Cardiometabolic parameters were not associated with 25(OH)D, even after adjusted by body composition variables. However, the high prevalence of hypovitaminosis D (75%) and the negative association between 25(OH)D and body composition reinforce the importance of analyzing and monitoring vitamin D status in this population.

Influences of Vitamin D and Iron Status on Skeletal Muscle Health: A Narrative Review

There is conflicting evidence of the roles vitamin D and iron have in isolation and combined in relation to muscle health. The purpose of this narrative review was to examine the current literature on the roles that vitamin D and iron have on skeletal muscle mass, strength, and function and how these nutrients are associated with skeletal muscle health in specific populations. Secondary purposes include exploring if low vitamin D and iron status are interrelated with skeletal muscle health and chronic inflammation and reviewing the influence of animal-source foods rich in these nutrients on health and performance. PubMed, Scopus, SPORT Discus, EMBAE, MEDLINE, and Google Scholar databases were searched to determine eligible studies. There was a positive effect of vitamin D on muscle mass, particularly in older adults. There was a positive effect of iron on aerobic and anaerobic performance. Studies reported mixed results for both vitamin D and iron on muscle strength and function. While vitamin D and iron deficiency commonly occur in combination, few studies examined effects on skeletal muscle health and inflammation. Isolated nutrients such as iron and vitamin D may have positive outcomes; however, nutrients within food sources may be most effective in improving skeletal muscle health.

Vitamin D Impacts on Skeletal Muscle Dysfunction in Patients with COPD Promoting Mitochondrial Health

Skeletal muscle dysfunction is frequently associated with chronic obstructive pulmonary disease (COPD), which is characterized by a permanent airflow limitation, with a worsening respiratory disorder during disease evolution. In COPD, the pathophysiological changes related to the chronic inflammatory state affect oxidant–antioxidant balance, which is one of the main mechanisms accompanying extra-pulmonary comorbidity such as muscle wasting. Muscle impairment is characterized by alterations on muscle fiber architecture, contractile protein integrity, and mitochondrial dysfunction. Exogenous and endogenous sources of reactive oxygen species (ROS) are present in COPD pathology. One of the endogenous sources of ROS is represented by mitochondria. Evidence demonstrated that vitamin D plays a crucial role for the maintenance of skeletal muscle health. Vitamin D deficiency affects oxidative stress and mitochondrial function influencing disease course through an effect on muscle function in COPD patients. This review will focus on vitamin-D-linked mechanisms that could modulate and ameliorate the damage response to free radicals in muscle fibers, evaluating vitamin D supplementation with enough potent effect to contrast mitochondrial impairment, but which avoids potential severe side effects.

Effects of branched-chain amino acid-rich supplementation on EWGSOP2 criteria for sarcopenia in older adults: a systematic review and meta-analysis

PURPOSE

According to criteria recommended by the European Working Group on Sarcopenia in Older People 2 (EWGSOP2), we analyzed the effects of branched-chain amino acid (BCAA)-rich supplements on muscle strength, muscle mass, and physical performance in older people.

METHODS

We searched PubMed, Embase, Cochrane Library, and CINAHL from inception until March 2021. Randomized controlled trials that examined the effect of BCAA-rich supplements on older people were included. Random-effects meta-analyses and sensitivity analyses were performed. Subgroup analyses were stratified by participant and supplementation characteristics. Meta-regression analyses were performed to examine the effect of continuous variables.

RESULTS

Thirty-five studies were included in this meta-analysis. Quality assessment revealed that 14 of 35 RCTs had some potential bias. The overall standardized mean difference (SMD) in muscle strength, muscle mass, and physical performance between the supplement and control groups was 0.35 (95% CI = [0.15, 0.55], P = 0.0007), 0.25 (95% CI = [0.10, 0.40], P = 0.0008), and 0.29 (95% CI = [0.00, 0.57], P = 0.05), respectively. Subgroup analysis revealed that essential amino acid supplementation improved handgrip strength more significantly than whey protein supplementation in older people. Meta-regression analysis revealed a significant linear relationship between improvements in handgrip strength and body mass index.

CONCLUSIONS

BCAA-rich supplementation by older people may have beneficial effects on muscle mass and strength. However, the included studies had high heterogeneity, and the results must be interpreted with caution.

PROSPERO REGISTRATION NUMBER

CRD42020206674.

In vitro Effects of Biologically Active Vitamin D on Myogenesis: A Systematic Review

Vitamin D (VD) deficiency is associated with muscle weakness. A reduction in the incidence of falls in the elderly following VD supplementation and identification of the VD receptor within muscle cells suggests a direct effect of VD on muscle, but little is known about the underlying mechanisms. Here we systematically searched the literature to identify effects of active VD [1,25(OH)2D3] on skeletal muscle myogenesis in vitro, with no restriction on year of publication. Eligibility was assessed by strict inclusion/exclusion criteria and agreed by two independent investigators. Twelve relevant pa-pers were identified using four different cell types (C2C12, primary mouse satellite cells, primary chick myoblasts, and primary human myoblasts) and a range of myogenic markers (myoD, myogenin, creatine kinase, myosin heavy chain, and myotube size). A clear inhibitory effect of 1,25(OH)2D3 on proliferation was reported, while the effects on the different stages of differentiation were less consistent probably due to variation in cell type, time points and doses of 1,25(OH)2D3 used. However, myotube size was consistently increased by 1,25(OH)2D3. Overall, the evidence suggests that 1,25(OH)2D3 inhibits proliferation and promotes differentiation of myoblasts, but future studies should use time courses to gain a clearer understanding.

Comparative analysis of the association between various serum vitamin D biomarkers and sarcopenia

Background

Vitamin D status is associated with muscle strength and maintenance of muscle fibers. However, which serum vitamin D biomarker better reflects sarcopenia remains unclear. The aim of this study was to investigate associations between various serum vitamin D biomarkers (total 25‐hydroxy vitamin D [25(OH)D], bioavailable 25(OH)D, 24,25‐dihydroxyvitamin D [24,25(OH)₂D], and vitamin D metabolite ratio [VMR]) and sarcopenia.

Methods

The data for 83 hip fracture patients were finally included in the analysis. Sarcopenia was defined according to the Asia Working Group for Sarcopenia (AWGS) criteria. Measurements of 24,25(OH)₂D and 25(OH)D were made using solid‐phase extraction (SPE) and subsequent liquid chromatography‐tandem mass spectrometry (LC‐MS/MS). Vitamin D binding protein (VDBP) concentration was measured using an enzyme‐linked immunosorbent assay. The VMR was calculated by dividing serum 24,25(OH)₂D by serum 25(OH)D and then multiplying by 100. Based on total 25(OH)D, VDBP, and albumin concentrations, bioavailable 25(OH)D concentrations were calculated using the equations from the other previous studies.

Results

Bioavailable 25(OH)D levels were significantly (p = 0.030) decreased in the sarcopenia group compared with the non‐sarcopenia group. Results of ROC analysis for the diagnosis of sarcopenia using serum level of bioavailable of 25(OH)D revealed that the cutoff point for bioavailable 25(OH)D was 1.70 ng/ml (AUC = 0.649, p < 0.001). In the group with a bioavailable 25(OH)D less than 1.70 ng/ml, the incidence of sarcopenia increased by 3.3 times (odds ratio: 3.33, p = 0.013).

Conclusion

We demonstrated that bioavailable 25(OH)D was associated with sarcopenia among the various serum vitamin D biomarkers. Bioavailable vitamin D might be helpful for assessing the risk of sarcopenia.

Associations of Vitamin D Levels with Physical Fitness and Motor Performance; A Cross-Sectional Study in Youth Soccer Players from Southern Croatia

Simple Summary

Vitamin D is a fat-soluble prohormone crucial for bone mineralization, muscle contractility, and neurological conductivity. It is theorized that Vitamin D plays an important role in sport performances, especially in young athletes. In this study we examined the associations of levels of 25-hydroxyvitamin D (25(OH)D) with physical fitness and motor-performance achievements in youth soccer players from Southern Croatia. Participants were tested on physical fitness, motor performance and vitamin D at the end of the winter period, when levels of vitamin D are known to be lowest due to low exposure to sunlight. Results showed that deficiency of 25(OH)D was widespread among youth soccer players living in Southern Croatia. Low 25(OH)D levels were associated with lower results in fitness tests (i.e., tests of energetic capacities), but there was no correlation between 25(OH)D levels and the results in motor performance tests (i.e., skill tests). Our results support the theory of the association between vitamin D and energetic capacities of athletes, but there is no evidence on association between vitamin D and skill-based capacities.

Abstract

Vitamin D level is known to be a factor potentially influencing physical fitness, but few studies have examined this phenomenon among youth athletes. We aimed to evaluate the associations of vitamin D levels (as measured by 25-hydroxyvitamin D concentrations—25(OH)D) with various physical fitness and motor performance tests in youth football (soccer) players. This cross-sectional study included a total of 52 youth soccer players (15.98 ± 2.26 years old) from Southern Croatia. The participants were evaluated at the end of the winter period and data were collected of anthropometric measures (body mass and body height), vitamin D status (25(OH)D levels), physical fitness tests (sprints of 10 and 20 m, 20 yards test, the countermovement jump, the reactive strength index (RSI)) and motor performance tests (the soccer-specific CODS, the soccer-specific agility, and static balance). Among the studied players, 54% had 25(OH)D insufficiency/deficiency, showing a lack of 25(OH)D is widespread even in youth athletes living at a southern latitude. The 25(OH)D level was correlated with sprint 20 m, 20 yards tests, and RSI, showing a greater role of 25(OH)D in physical fitness tests where energetic capacity is essential than in sport-related motor performance tests where skills are crucial. Our results support the idea that vitamin D can play a determinant role in physical fitness tests with a clear physiological component, but is not crucial in motor performance tests related to specific sports where skills are a key component. Future studies should investigate the effects of vitamin D supplementation on the performance in physical fitness and motor performance tests among youth athletes.

Sarcopenia and Vitamin D Deficiency in Patients with Crohn's Disease: Pathological Conditions That Should Be Linked Together

Sarcopenia is a prevalent condition in patients with Crohn’s disease (CD), representing an independent predictor factor for the development of major postoperative complications. Thus, a proper assessment of the muscle strength, by using different validated tools, should be deemed an important step of the clinical management of these patients. Patients with CD are frequently malnourished, presenting a high prevalence of different macro- and micro-nutrient deficiencies, including that of vitamin D. The available published studies indicate that vitamin D is involved in the regulation of proliferation, differentiation, and regeneration of muscle cells. The relationship between vitamin D deficiency and sarcopenia has been extensively studied in other populations, with interesting evidence in regards to a potential role of vitamin D supplementation as a means to prevent and treat sarcopenia. The aim of this review was to find studies that linked together these pathological conditions.

Vitamin D Promotes Skeletal Muscle Regeneration and Mitochondrial Health

Vitamin D is an essential nutrient for the maintenance of skeletal muscle and bone health. The vitamin D receptor (VDR) is present in muscle, as is CYP27B1, the enzyme that hydroxylates 25(OH)D to its active form, 1,25(OH)D. Furthermore, mounting evidence suggests that vitamin D may play an important role during muscle damage and regeneration. Muscle damage is characterized by compromised muscle fiber architecture, disruption of contractile protein integrity, and mitochondrial dysfunction. Muscle regeneration is a complex process that involves restoration of mitochondrial function and activation of satellite cells (SC), the resident skeletal muscle stem cells. VDR expression is strongly upregulated following injury, particularly in central nuclei and SCs in animal models of muscle injury. Mechanistic studies provide some insight into the possible role of vitamin D activity in injured muscle. In vitro and in vivo rodent studies show that vitamin D mitigates reactive oxygen species (ROS) production, augments antioxidant capacity, and prevents oxidative stress, a common antagonist in muscle damage. Additionally, VDR knockdown results in decreased mitochondrial oxidative capacity and ATP production, suggesting that vitamin D is crucial for mitochondrial oxidative phosphorylation capacity; an important driver of muscle regeneration. Vitamin D regulation of mitochondrial health may also have implications for SC activity and self-renewal capacity, which could further affect muscle regeneration. However, the optimal timing, form and dose of vitamin D, as well as the mechanism by which vitamin D contributes to maintenance and restoration of muscle strength following injury, have not been determined. More research is needed to determine mechanistic action of 1,25(OH)D on mitochondria and SCs, as well as how this action manifests following muscle injury in vivo. Moreover, standardization in vitamin D sufficiency cut-points, time-course study of the efficacy of vitamin D administration, and comparison of multiple analogs of vitamin D are necessary to elucidate the potential of vitamin D as a significant contributor to muscle regeneration following injury. Here we will review the contribution of vitamin D to skeletal muscle regeneration following injury.

Vitamin D supplementation does not enhance resistance training-induced gains in muscle strength and lean body mass in vitamin D deficient young men

PURPOSE

Vitamin D (Vit-D) supplementation has been shown to increased muscle strength in young adults. It remains unclear if Vit-D supplementation enhances the efficacy of resistance training (RT). This study tested the hypothesis that Vit-D supplementation would enhance the RT-induced increases in muscle strength and lean body mass (LBM) in Vit-D deficient young men.

METHODS

Thirty-nine men (baseline serum 25(OH)D < 50 nmol L^‒1) were quasi-randomly assigned to one of the two groups that performed a 12-week supervised RT program concomitant with either Vit-D (8000 IU daily; VD) or placebo (PLC) supplementation.

RESULTS

During 12-week RT, energy and nutrient (except Vit-D) intake and training loads did not differ in the two groups. Serum 25(OH)D levels increased from 36.3 ± 9.2 to 142.4 ± 21.9 nmol L^‒1 (P < 0.05) in VD group and remained unchanged between 36.3 ± 8.9 and 29.4 ± 6.6 nmol L^‒1 (P > 0.05) in PLC group. Muscle strength (1-repetition maximum) increased (P < 0.05) to an equal extent in the two groups in 5 exercises performed on RT equipment, whereas strength gains in chest press and seated row were greater (P < 0.05) in PLC compared to VD group. Total and regional LBM (measured by DXA scan) increased (P < 0.05) equally in the two groups. Android fat mass decreased (P < 0.05) in VD group only.

CONCLUSION

Vit-D supplementation does not enhance the efficacy of RT in terms of muscle strength and LBM gains in Vit-D deficient young healthy men.

Vitamin D Deficiency is Associated with Handgrip Strength, Nutritional Status and T2DM in Community-Dwelling Older Mexican Women: A Cross-Sectional Study

The aim of this study was to evaluate the association between handgrip strength, nutritional status and vitamin D deficiency in Mexican community-dwelling older women. A cross sectional study in women ≥ 60 years-old was performed. Plasma 25-hydroxyvitamin D (25(OH)D) concentrations were measured by a quantitative immunoassay technique. Handgrip strength was assessed using a dynamometer, while nutritional status was assessed through the Full Mini Nutritional Assessment (Full-MNA). A total of 116 women participated in the study, their mean age was 70.3 ± 5.8 years; 49.1% of the study group had plasma 25(OH)D levels lower than 40 nmol/L [16 ng/mL]. Meanwhile, 28.45% of participants had low handgrip strength (<16 kg), and 23.1% were identified at risk of malnutrition/malnourished according with Full-MNA score. Women with 25(OH)D deficiency (<40 nmol/L [16 ng/mL]) were more likely to have low handgrip strength (OR = 2.64, p = 0.025) compared with those with higher 25(OH)D values. Additionally, being malnourished or at risk of malnutrition (OR = 2.53, p = 0.045) or having type 2 diabetes mellitus (T2DM) (OR = 2.92, p = 0.044) was also associated with low 25(OH)D. The prevalence of low plasma 25(OH)D concentrations was high among Mexican active older women. Low handgrip strength, being at risk of malnutrition/malnourished, or diagnosed with T2DM was also associated with Vitamin D deficiency.

Role of hormones in sarcopenia

Aging involves numerous changes in body composition that include a decrease in skeletal muscle mass. The gradual reduction in muscle mass is associated with a simultaneous decrease in muscle strength, which leads to reduced mobility, fragility and loss of independence. This process called sarcopenia is secondary to several factors such as sedentary lifestyle, inadequate nutrition, chronic inflammatory state and neurological alterations. However, the endocrine changes associated with aging seem to be of special importance in the development of sarcopenia. On one hand, advancing age is associated with a decreased secretion of the main hormones that stimulate skeletal muscle mass and function (growth hormone, insulin-like growth factor 1 (IGFI), testosterone and estradiol). On the other hand, the alteration of the IGF-I signaling along with decreased insulin sensitivity also have an important impact on myogenesis. Other hormones that decline with aging such as the adrenal-derived dehydroepiandrosterone, thyroid hormones and vitamin D seem to also be involved in sarcopenia. Adipokines released by adipose tissue show important changes during aging and can affect muscle physiology and metabolism. In addition, catabolic hormones such as cortisol and angiotensin II can accelerate aged-induced muscle atrophy, as they are involved in muscle wasting and their levels increase with age. The role played by all of these hormones and the possible use of some of them as therapeutic tools for treating sarcopenia will be discussed.

Low Serum 25-Hydroxyvitamin D Levels Are Related to Frailty and Sarcopenia in Patients with Chronic Liver Disease

Low vitamin D status is related to frailty and/or sarcopenia in elderly individuals. However, these relationships are unclear in patients with chronic liver disease (CLD). This study aimed at exploring the relationship between serum 25-hydroxyvitamin D [25(OH)D] levels and frailty or sarcopenia in 231 patients with CLD. Frailty was determined based on five factors (weight loss, low physical activity, weakness, slowness, and exhaustion). Sarcopenia was diagnosed by applying the Japan Society of Hepatology criteria. The patients were classified into three groups according to baseline 25(OH)D levels: low (L), intermediate (I), and high (H) vitamin D (VD) groups. Of the 231 patients, 70 (30.3%) and 66 (28.6%) had frailty and sarcopenia, respectively. The prevalence rate of frailty and sarcopenia significantly increased stepwise with a decline in the vitamin D status. The L-VD group showed the highest prevalence rates of frailty and sarcopenia (49.1% (28/57), p < 0.001 for both), whereas the H-VD group showed the lowest prevalence rates of frailty (15.3% (9/59)) and sarcopenia (18.6% (11/59)) (p < 0.001 for both). Multivariate analysis identified serum 25(OH)D levels as a significant independent factor related to frailty and sarcopenia. Serum 25(OH)D levels significantly correlated with handgrip strength, skeletal muscle mass index, and gait speed. In conclusion, low serum vitamin D level, especially severe vitamin D deficient status, is closely related to frailty and sarcopenia in patients with CLD.

Prevalence of Vitamin D Insufficiency and Deficiency in Young, Female Patients With Lower Extremity Musculoskeletal Complaints

BACKGROUND

Low levels of vitamin D have well-known impacts on bone health, but vitamin D also has a more global role throughout many tissues, including skeletal muscle. The high prevalence of hypovitaminosis D and the vast physiological features of vitamin D have led researchers to examine the influence of vitamin D on physical performance and injury. Because of the critical role of vitamin D in maintaining musculoskeletal health and function, a high rate of hypovitaminosis D among female patients with a variety of musculoskeletal issues could be of high clinical relevance.

HYPOTHESIS

There is a high prevalence of low vitamin D in female patients with both acute and overuse sports-related issues of both soft tissue and bone.

STUDY DESIGN

Prospective cohort study.

LEVEL OF EVIDENCE

Level 3.

METHODS

Female patients, aged 16 to 40 years, presenting with lower extremity injury diagnosed within the past 4 weeks, no use of multivitamin or vitamin D supplement, and no history of malabsorption syndrome met the inclusion criteria. Vitamin D levels were assessed and categorized as normal (≥32 ng/mL) and low, which includes insufficient (20.01-31.9 ng/mL) and deficient (≤20 ng/mL).

RESULTS

Of the 105 patients enrolled, 65.7% had low vitamin D. Within the low vitamin D cohort, 40.6% were deficient and 59.4% were insufficient. Injuries were grouped into overuse or acute with 74 overuse injuries and 31 acute injuries, exhibiting low vitamin D prevalence of 60.8% and 77.4%, respectively. Patients with ligamentous/cartilaginous injuries exhibited the highest percentage of low vitamin D (76.5%), followed by those with patellofemoral-related complaints (71.0%), muscle/tendon injuries (54.6%), and bone stress injuries (45.5%). In univariable analysis, older age, non-White race, less physical activity, less high-intensity interval training days, less endurance training days, and more rest days showed an association with low vitamin D, but none showed an independent association in multivariable analysis.

CONCLUSION

The prevalence of low vitamin D in female patients with various musculoskeletal complaints was high. Clinicians should evaluate for low vitamin D in both acute and overuse injuries.

CLINICAL RELEVANCE

In addition to screening, this study suggests that clinicians should evaluate for low vitamin D levels beyond bone stress injuries in the setting of acute and overuse injuries.

Vitamin D3 content of cows' milk produced in Northern Ireland and its efficacy as a vehicle for vitamin D fortification: a UK model

Cows' milk is a relatively poor source of vitamin D but figures listed in UK food composition tables may be outdated. Samples of milk were collected for 1-year and vitamin D₃ concentrations analysed using HPLC. Milk consumption data were obtained from the National Diet and Nutrition Survey (Years 1-4). A theoretical model applied vitamin D₃ fortifications of 1 μg, 1.5 μg and 2 μg/100g to simulate improvements in vitamin D intakes. Mean ± SD vitamin D₃ in whole milk was 0.06 ± 0.02 μg/100g. No seasonal differences were apparent. Fortification of cows' milks with 1 μg, 1.5 μg and 2.0 μg/100g, theoretically increased median vitamin D intakes from 2.0 μg/day to 4.2 μg, 5.1 μg and 5.9 μg/day, respectively. Higher vitamin D₃ in milk from this study than that currently in food composition tables, suggests further analysis is warranted. This model suggests vitamin D fortification of cows' milk is an effective strategy to help more of the population achieve recently revised RNIs for vitamin D.

The vitamin D activator CYP27B1 is upregulated in muscle fibers in denervating disease and can track progression in amyotrophic lateral sclerosis

Extra-renal expression of Cytochrome P450 Family 27 Subfamily B Member 1 (CYP27B1) has been well recognized and reflects the importance of intracrine/paracrine vitamin D signaling in different tissues under physiological and pathological conditions. In a prior RNA sequencing project, we identified CYP27B1 mRNA as upregulated in muscle samples from patients with amyotrophic lateral sclerosis (ALS) compared to normal controls. Our aims here were: (1) to validate this finding in a larger sample set including disease controls, (2) to determine which cell type is expressing CYP27B1 protein in muscle tissue, (3) to correlate CYP27B1 mRNA expression with disease progression in the SOD1G93A ALS mouse and in ALS patients. We assessed CYP27B1 expression by qPCR, western blot, and immunohistochemistry in a repository of muscle samples from ALS, disease controls (myopathy and non-ALS neuropathic disease), normal subjects, and muscle samples from the SOD1G93A mouse. Eight ALS patients were studied prospectively over 6-12 months with serial muscle biopsies. We found that CYP27B1 mRNA and protein levels were significantly increased in ALS versus normal and myopathy muscle samples. Neuropathy samples had increased CYP27B1 mRNA and protein expression but at a lower level than the ALS group. Immunohistochemistry showed that CYP27B1 localized to myofibers, especially those with features of denervation. In the SOD1G93A mouse, CYP27B1 mRNA and protein were detected in skeletal muscle in early pre-symptomatic stages and increased through end-stage. In the human study, increases in CYP27B1 mRNA in muscle biopsies correlated with disease progression rates over the same time period. In summary, we show for the first time that CYP27B1 mRNA and protein expression are elevated in muscle fibers in denervating disease, especially ALS, where mRNA levels can potentially serve as a surrogate marker for tracking disease progression. Its upregulation may reflect a local perturbation of vitamin D signaling, and further characterization of this pathway may provide insight into underlying molecular processes linked to muscle denervation.

Is vitamin D status reflected by testosterone concentration in elite athletes?

Vitamin D is a nutrient whose active form affects tissues as a hormone and possibly enhances performance. One plausible mechanism is by increasing testosterone concentration, which is established as an important factor for athletic performance. Therefore the aim of the study was to examine the relationship between plasma concentration of 25(OH)D and testosterone in Polish elite track and field athletes depending on vitamin D status, season, training period, body composition, sex, type of training, sun exposure and vitamin D supplementation. Plasma concentrations of 25(OH)D and testosterone were measured in all seasons within two years in athletes (70 females, 79 males) who represent strength (n = 103) and endurance (n = 46) kinds of sports, in the preparatorycompetitive season and transition period. There were no differences in 25(OH)D concentration between male and female athletes, insufficiency [25(OH)D < 30 ng/ml] was observed in 32.9%, whereas deficiency [25(OH)D < 20 ng/ ml] in 3.2%. Circannual rhythm was noted for vitamin D but not for testosterone concentration; no correlations between them were found either in strength or endurance athletes or between 25(OH)D and body composition. Testosterone concentration was higher in the transition period than in the preparatory-competition period only in male athletes. Higher 25(OH)D was observed in athletes who trained during winter in Africa (higher sun exposure) or used oral supplementation, whereas the respective testosterone levels were unchanged. In athletes, testosterone concentration did not reflect vitamin D status. The widespread of inadequate vitamin D status among athletes, makes it vital to recommend them the regular monitoring of 25(OH)D concentration and use of reasonable supplementation.

Decreased Serum Adiponectin Reflects Low Vitamin D, High Interleukin 6, and Poor Physical Performance in Knee Osteoarthritis

Obesity is a major contributor to deterioration of physical function toward sarcopenia in knee osteoarthritis (OA) due to its effect mediated through adipokines-derived molecules that have pro-/anti-inflammatory properties. This study aimed to investigate relationships of serum adiponectin, 25-hydroxyvitamin D (25(OH)D), interleukin (IL)-6, and physical performance in knee OA patients. A total of 175 knee OA patients and 52 healthy controls were recruited. Serum adiponectin, 25(OH)D, IL-6, biochemical markers, knee pain and functional scores, muscle strength, physical performance, metabolic parameters, and body composition were evaluated. Serum adiponectin levels were significantly higher in knee OA patients than that in controls, while its serum levels were significantly decreased in obese patients, especially those with sarcopenia. Furthermore, there were independent relationships of serum adiponectin with body composition parameters, knee pain scores, physical function tests, and metabolic parameters in knee OA patients. Besides, serum adiponectin levels were positively associated with 25(OH)D levels, and negatively correlated with C-reactive protein and IL-6 levels in knee OA. Additionally, low serum adiponectin could be used to distinguish knee OA patients with sarcopenic obesity from those without sarcopenic obesity. Circulating adiponectin levels may serve as a possible surrogate biomarker for exacerbated physical function in knee OA patients-particularly sarcopenic obesity.

Vitamin D in the Foot and Ankle: A Review of the Literature

BACKGROUND

Vitamin D is an essential vitamin that targets several tissues and organs and plays an important role in calcium homeostasis. Vitamin D deficiency is common, particularly at higher latitudes, where there is reduced exposure to ultraviolet B radiation. We reviewed the role of vitamin D and its deficiency in foot and ankle pathology.

METHODS

The effects of vitamin D deficiency have been extensively studied, but only a small portion of the literature has focused on the foot and ankle. Most evidence regarding the foot and ankle consists of retrospective studies, which cannot determine whether vitamin D deficiency is, in fact, the cause of the pathologies being investigated.

RESULTS

The available evidence suggests that insufficient vitamin D levels may result in an increased incidence of foot and ankle fractures. The effects of vitamin D deficiency on fracture healing, bone marrow edema syndrome, osteochondral lesions of the talus, strength around the foot and ankle, tendon disorders, elective foot and ankle surgery, and other foot and ankle conditions are less clear.

CONCLUSIONS

Based on the available evidence, we cannot recommend routine testing or supplementation of vitamin D in patients with foot and ankle pathology. However, supplementation is cheap, safe, and may be of benefit in patients at high risk for deficiency. When vitamin D is supplemented, the evidence suggests that calcium should be co-supplemented. Further high-quality research is needed into the effect of vitamin D in the foot and ankle. Cost-benefit analyses of routine testing and supplementation of vitamin D for foot and ankle pathology are also required.

The Association between Serum Levels of 25[OH]D, Body Weight Changes and Body Composition Indices in Patients with Heart Failure

We try to determine the association between weight changes (WC), both loss or gain, body composition indices (BCI) and serum levels of 25[OH]D during heart failure (HF). WC was determined in 412 patients (14.3% female, aged: 53.6 ± 10.0 years, NYHA class: 2.5 ± 0.8). Body fat, fat percentage and fat-free mass determined by dual energy X-rays absorptiometry (DEXA) and serum levels of 25[OH]D were analyzed. Logistic regression was used to calculate odds ratios for 25[OH]D insufficiency (<30 ng/mL) or deficiency (<20 ng/mL) by quintiles of WC, in comparison to weight-stable subgroup. The serum 25[OH]D was lower in weight loosing than weight stable subgroup. In fully adjusted models the risk of either insufficient or deficient 25[OH]D levels was independent of BCI and HF severity markers. The risk was elevated in higher weight loss subgroups but also in weight gain subgroup. In full adjustment, the odds for 25[OH]D deficiency in the top weight loss and weight gain subgroups were 3.30; 95%CI: 1.37–7.93, p = 0.008 and 2.41; 95%CI: 0.91–6.38, p = 0.08, respectively. The risk of 25[OH]D deficiency/insufficiency was also independently associated with potential UVB exposure, but not with nutritional status and BCI. Metabolic instability in HF was reflected by edema-free WC, but not nutritional status. BCI is independently associated with deficiency/insufficiency of serum 25[OH]D.

1α, 25(OH)2D3 regulates agrin-induced acetylcholine receptor clustering through upregulation of rapsyn expression in C2C12 myotubes

The active form of vitamin D (1α, 25-dihydroxyvitamin D3 [1α, 25(OH)2D3], referred to as 1,25D) has been suggested to play a pivotal role in skeletal muscle function and metabolism. However, the mechanisms through which 1,25D functions in this tissue remain to be elucidated. Recent studies have shown that vitamin D signaling regulates neuromuscular maintenance and improves locomotion in mice. In the present study, we examined the effects of 1,25D on neuromuscular synaptogenesis by measuring clustering of acetylcholine receptors (AChRs) in C2C12 myotubes. 1,25D treatment enhanced the agrin-induced AChR clustering in myotubes compared to treatment with agrin alone. Furthermore, siRNA-mediated knockdown of the vitamin D receptor (VDR) decreased the agrin-induced AChR clustering. 1,25D increased the expression of rapsyn, which is necessary for AChR clustering, while demonstrating no effect on other neuromuscular junction-related genes. In addition, rapsyn expression was dependent on 1,25D-VDR signaling. These results suggest that 1,25D-VDR signaling may regulate rapsin expression, resulting in the up-regulation of agrin-induced AChR clustering.

Vitamin D supplementation after the menopause

The purpose of this review was to assess recent evidence regarding the effects of low vitamin D levels on some highly prevalent clinical conditions of postmenopausal women. We reviewed and selected recent literature regarding menopause-related conditions associated with vitamin D deficiency and interventions to manage them. Low circulating 25-hydroxyvitamin D (25(OH)D) levels related to menopause are linked to diet, lifestyle, changes in body composition, insulin sensitivity, and reduced physical activity. Vitamin D supplementation increases serum 25(OH)D levels while normalizing parathyroid hormone and bone markers, and in women with serum 25(OH)D levels below 10 ng/ml supplementation may improve bone mineral density. Low vitamin D status has been associated with the metabolic syndrome, high triglyceride levels, and low high-density lipoprotein cholesterol levels. When compared with placebo, vitamin D supplementation may lower the risk of the metabolic syndrome, hypertriglyceridemia, and hyperglycemia. There is an inverse relationship between fat mass and serum 25(OH)D levels and, therefore, the dosage of supplementation should be adjusted according to the body mass index. Although vitamin D supplementation may improve glucose metabolism in prediabetic subjects, data regarding muscle strength are conflictive. There is evidence that vitamin D over-treatment, to reach extremely high circulating 25(OH)D levels, does not result in better clinical outcomes. The identification and treatment of vitamin D deficiency in postmenopausal women may improve their general health and health outcomes. Vitamin D supplementation should preferably be based on the use of either cholecalciferol or calcifediol.

Vitamin D Deficiency and Sarcopenia in Older Persons

Vitamin D deficiency is a common health problem worldwide, in particular among older people. Vitamin D regulates and modulates the physiology and function of multiple human systems, including the skeletal muscle. The effect of vitamin D on the muscle has been widely investigated, suggesting that this hormone can stimulate the proliferation and differentiation of skeletal muscle fibers, maintaining and improving muscle strength and physical performance. Older persons have a higher prevalence of low Vitamin D levels as a consequence of low dietary intake and reduced ultraviolet irradiation of the skin. Therefore, older people with vitamin D deficiency might be at risk of sarcopenia, a geriatric syndrome characterized by the progressive loss of skeletal muscle mass and strength often complicated by adverse events, such as falls, disability hospitalization and death. Several randomized clinical trials have been conducted to investigate the effect of oral vitamin D supplementation in older patients to prevent or treat sarcopenia, but results are still controversial. In this narrative review we summarize the biological, clinical and epidemiological evidence supporting the hypothesis of a causal association between Vitamin D deficiency and an increased risk of sarcopenia in older people.

A single mega dose of vitamin D3 improves selected physical variables in vitamin D-deficient young amateur soccer players: a randomized controlled trial

This randomized controlled trial aimed to test whether vitamin D (VD) supplementation affects measures of physical performance in VD-deficient, mildly trained children. Thirty-six recreationally soccer player boys were randomly assigned to single dose (200 000 IU) of VD3 (n = 19) or placebo (n = 17). Plasma 25-hydroxyvitamin D (25-OHD) was assessed and measures of physical performance (i.e., vertical and standing broad jumps, triple hop, 10-m and 30-m sprints, shuttle run) were performed before and 12 weeks after the loading dose. Mixed ANCOVA models were performed and effect size was estimated by partial eta squared (η_p²). Baseline 25-OHD and physical variables were equivalent in the 2 groups. Twelve weeks after VD loading, plasma 25-OHD increased and physical variables improved only in the VD group. There was a significant interaction effects for group by time for vertical jump (F = 14.9, p = 0.001, η_p² = 0.394), triple hop jump (F = 24.2, p < 0.001, η_p² = 0.513), 10-m (F = 4.46, p = 0.046, η_p² = 0.162) and 30-m (F = 6.56, p = 0.017, η_p² = 0.222) sprints, and shuttle run (F = 13.4, p = 0.001, η_p² = 0.369). In conclusion, a single bolus of VD3 resulted in significant improvements in jumping ability, agility, and running speed in mildly trained children that are deficient in VD. The findings suggest that correcting VD deficit might be beneficial for physical performance. Novelty A mega dose of VD3 improves jumping ability, agility, and running speed in VD-deficient, mildly trained children. Effect of VD on measures of physical performance is noticeable 3 months after the loading dose.

Admission 25-Hydroxyvitamin D Levels Are Associated With Functional Status at Time of Discharge from Intensive Care Unit in Critically Ill Surgical Patients

BACKGROUND

Vitamin D status is associated with length of stay (LOS) and discharge destination in critically ill patients. To further understand this relationship, we investigated whether admission 25-hydroxyvitaminD (25OHD) levels are associated with discharge functional status in the intensive care unit (ICU).

METHODS

In this retrospective study, data from 2 surgical ICUs at a large teaching hospital were analyzed. 25OHD levels were measured within 24 hours of ICU admission and Functional Status Score for the ICU (FSS-ICU) was calculated within 24 hours of ICU discharge for all patients. To investigate the association of vitamin D status with FSS-ICU, we constructed linear and logistic regression models, controlling for body mass index, Nutrition Risk in the Critically Ill score, ICU LOS, and cumulative protein or caloric deficit during ICU admission.

RESULTS

Mean 25OHD level and FSS-ICU was 19 (SD 8) ng/mL and 17 (SD 4), respectively, in the analytic cohort (n = 300). Each unit increase in 25OHD level was associated with a 0.2 increment in FSS-ICU (β = .20; 95% CI 0.14-0.25). Patients with 25OHD levels <20 ng/mL had >3-fold risk of low FSS-ICU (<17) compared with patients with 25OHD >20 ng/mL (OR 3.45; 95% CI 1.96-6.08).

CONCLUSIONS

Our results suggest that vitamin D status at admission is associated with discharge FSS-ICU in critically ill surgical patients. Future studies are needed to validate our results, to build upon our findings, and to determine whether optimizing 25OHD levels can improve functional status and other important clinical outcomes in ICU patients.

Expression levels of selected cytokines and microRNAs in response to vitamin D supplementation in ultra-marathon runners

Ultra-marathon (UM) running is an extreme endurance exercise. However, the mechanisms triggered with its practice remain unclear. While it is documented that strenuous physical activity activates immune responses and vitamin D plays a role in immune system suppression, data on the relationship between vitamin D status and cytokine profile in athletic populations are limited. To analyse the relative mRNA expression levels of selected pro-inflammatory cytokines (IL-1β, IL-6, IL-8, IL-17, TNF-α), COX-2, vitamin D receptor and abundance of selected inflammatory microRNAs (Hsa-miR-21, -miR-146a, -miR-150, -miR-155, -miR-222, -miR-223) before and after a 100 km race in amateur runners in the presence or absence of vitamin D supplementation. Twenty runners aged 36-40years were divided into two groups: with and without vitamin D3 supplementation (10,000units daily). Blood samples were collected before and 12 h after the UM. The mRNA expression levels of selected cytokines, COX-2 and VDR in peripheral blood and abundance of serum exosomal miRNAs were investigated using q-RT-PCR. After UM, the significant up-regulation of TNF-α and hsa-miR-155 and down-regulation of IL-1β were observed in the group with vitamin D supplementation. In its absence, hsa-miR-155 and -miR-223 were significantly up-regulated. Additionally, a reverse correlation was observed between IL-6 expression level and abundance of hsa-miR-155 and -miR-223 in both groups. No statistical differences were noted when the other miRNAs and genes were examined in the groups and at the time points. The UM-induced mRNA expression pattern of pro-inflammatory cytokines could be influenced by vitamin D supplementation and/or miRNA.

Surgical Considerations for Vitamin D Deficiency in Foot and Ankle Surgery

Vitamin D deficiency affects nearly one-sixth of the world's population and is common in patients undergoing foot and ankle surgery. Vitamin D is critical for calcium homeostasis and plays an important role in the maintenance of bone health. Patients undergoing foot and ankle procedures can be evaluated preoperatively with vitamin D level testing, and deficiencies can be addressed with either preoperative or postoperative supplementation. Current data suggest that patients with adequate vitamin D levels may have better outcomes, but the details are not yet clear. Vitamin D supplementation is well tolerated with rare side effects.

Vitamin D produces a perilipin 2-dependent increase in mitochondrial function in C2C12 myotubes

Vitamin D has been connected with increased intramyocellular lipid (IMCL) and has also been shown to increase mitochondrial function and insulin sensitivity. Evidence suggests that perilipin 2 (PLIN2), a perilipin protein upregulated with calcitriol treatment, may be integral to managing increased IMCL capacity and lipid oxidation in skeletal muscle. Therefore, we hypothesized that PLIN2 is required for vitamin D induced IMCL accumulation and increased mitochondrial oxidative function. To address this hypothesis, we treated C2C12 myotubes with 100 nM calcitriol (the active form of vitamin D) and/or PLIN2 siRNA in a four group design and analyzed markers of IMCL accumulation and metabolism using qRT-PCR, cytochemistry, and oxygen consumption assay. Expression of PLIN2, but not PLIN3 or PLIN5 mRNA was increased with calcitriol, and PLIN2 induction was prevented with siRNA knockdown without compensation by other perilipins. PLIN2 knockdown did not appear to prevent lipid accumulation. Calcitriol treatment increased mRNA expression of triglyceride synthesizing genes DGAT1 and DGAT2 and also lipolytic genes ATGL and CGI-58. PLIN2 knockdown decreased the expression of CGI-58 and CPT1, and was required for calcitriol-induced upregulation of DGAT2. Calcitriol increased oxygen consumption rate while PLIN2 knockdown decreased oxygen consumption rate. PLIN2 was required for a calcitriol-induced increase in oxygen consumption driven by mitochondrial complex II. We conclude that calcitriol increases mitochondrial function in myotubes and that this increase is at least in part mediated by PLIN2.